Math Gets Around: The Entomology of Civil Engineering

February 11, 2009

In the continuing saga of animals that are better than you at math, it now appears that ants are much better than most of us at optimization. Granted, they may not be able to think abstractly, but in concrete terms, they far surpass us with a particular type of optimization: the efficiency of traffic flow.

As anyone who has gone to a picnic will tell you, ants do a very good job of creating traffic streams - their foot traffic moves steadily, and without the major pileups to which my fellow residents of Los Angeles have become so accustomed. One could argue that the wide expanse of park area is proportionately much larger for the humble ant than what most motorists have to live with, but even so, the march of the ant colony often appears quite regimented, even with space enough to make a wider path. How is it that ants can control their traffic so well?

This article from the Wired Science blog discuss how ants succeed where we fail. At the heart of the matter is a study from the University of Sydney on leafcutter ants. In order to give the ants a better sense of what it's like trying to navigate through a congested urban landscape, scientists restricted the ants to naturally narrow pathways, such as the ends of tree branches, in order to better understand how these ants organize their traffic in cramped spaces.

The findings clash with most people's behavior on the freeway:

In the latest findings, published in the February issue of the Journal of Experimental Biology, [entomologist Audrey] Dussutour's team found that ants leaving the colony automatically gave right-of-way to those returning with food. Of the returning ants, some were empty-mandibled — but rather than passing their leaf-carrying, slow-moving brethren, they gathered in clusters and moved behind them.

Rather than try to outpace their slower moving brethren, those without loads to carry simply kept pace with the slower ants. This is at direct odds with what most people do on the roads - who wants to drive stuck behind a bus? Based on our own behavior, we may question the wisdom of the leaf cutter ant's process.

As is often the case, however, nature knows best. By not trying to barrel ahead of the slower moving ants, the ants without any baggage saved time on average. Not by a paltry amount, either - the study estimates "that patience reduced the average delay experienced by an individual ant crossing a crowded three-meter bridge from 64 to 32 seconds." That's a 50% reduction in commute time!

One plausible explanation for the difference between our behavior and the ant's behavior is that we are looking at different optimization problems. People in general are trying to minimize their own individual travel times, and the other cars on the road aren't given much consideration. With (apparently) smaller egos, the problem in the ant's case is to make the whole traffic network run as smoothly as possible, so food can be brought in quickly, and energy isn't wasted in traffic jams.

The study helps give weight to the maxim that patience is a virtue. Haste while driving carries with it certain risks, risks that on average far outweigh the benefits that come from not trying to outpace others on the road.

It's doubtful that this study will do much to change human behavior, but understanding efficient traffic flow algorithms certainly has its applications, from urban planning to the engineering of self-driving cars. Perhaps people would be more patient if they weren't the ones doing the driving.

Unfortunately, the days of the self driving car are not yet upon us, so until that day arrives, we must be content with what we have. So, dear reader, take a cue from the noble ant, and slow it down when you're on the road - over time, it may save you time.